Just about one year ago at this time (April 24, 2009), the first batch of strong to severe thunderstorms made their way across the region. Yes there were some severe thunderstorm warnings accompanied by reports of hail anywhere from penny to golf ball size and winds that caused downed trees, however this was one of the few days of active stormy weather in North Central Wisconsin in 2009.
We are still rather early into the 2010 severe storm season and thus far it has been fairly quiet. No less why not provide some insight into how often the Badger State is the target of severe thunderstorms and tornadoes. First off in an average year there are 30 to 40 days when thunderstorms rumble across the state. Of those storms that turn severe, nearly 54% produce damaging winds in excess of 58 mph, while 34% produce hail 1" in diameter or larger. Lower down on the list are storms that produce tornadoes at 6.5% of the time and just over 5% lead to flash flooding events. If you have resided in the Badger State for a number of years, it probably comes as no surprise that the southern third of the state has the greatest number of storms that produce hail and the higher concentration in general of severe storms on average. The peak season for severe storms to brew is from April through September and the most frequent time they occur is during the late afternoon or evening hours. Another fact that you may have heard before is that February is the only month in Wisconsin where there has not been a reported tornado. Checking the records, which go all the way back to 1844, the other cold weather months of November and December have featured 6 twisters each in total, while January has had only 3. On the flip side, June is typically the most active severe weather month, with a total of 416 tornadoes having been sighted in Wisconsin over the past 165 years.
This leads to one of the records in the Wisconsin weather book that our area holds the top 2 spots, largest hail stones to ever fall in the state. Coming in at #2 is the 5.5" diameter hail that pummeled Port Edwards on June 7, 2007. This supercell thunderstorm was a part of the same band of storms that produced tornadoes in Wisconsin Rapids, near Mosinee, and the 40 mile track twister that stretched from eastern Langlade County all the way into Marinette County in NE Wisconsin. However the largest sized hail to ever fall in Wisconsin took place on May 22, 1921 on the north side of Wausau, measuring 5.7" in diameter. Since many of us weren't around back in the early 1920s to remember this event first hand, I did some research through the American Meteorological Society online publication archives to get more details on how this hail storm unfolded.
Let me set the scene. It was a Sunday evening just after 7:30pm when a thunderstorm approached the Wausau area from the southwest. Initially flashes of lightning and some large raindrops accompanied this storm as it moved into Wausau. However at 8:03pm, the hail began to fall, ranging in size from walnuts to as large as oranges (1.25" to 3" in diameter). As the intensity of the hail storm peaked, the largest stones were up to 18" in circumference. If you do the math to determine the diameter, that works out to 5.7" in size from end to end. When the hail was examined more closely, it was found to have 6 to 7 layers of ice on it and was roughly spherical in appearance, with a few that looked like pin cushions. Interestingly the winds associated with this storm were relatively light at the surface, but obviously that was a different story up in the storm clouds, where those raindrops where being rapidly rotated vertically up through the storm, before finally growing so large that the hail stones fell to the ground. As you might suspect, quite a bit of damage was done by the hail in Wausau, with many trees looking like they had been pruned, while cars parked outside had their windows smashed, along with many dents not only on cars but also houses. Although several folks suffered minor injuries, there were not any serious injuries or deaths because of this storm. Considering the lack of any early warning system back in the 1920s of approaching storms, let alone having no real time radar or even television, it is amazing that no one died.
To read more about this historic hail storm in Wausau, check out the article that appeared in the June 1921 issue of the Monthly Weather Review. In addition, if you want to learn more about the effects of severe storms, tornadoes or any major weather events that impacted Wisconsin or the U.S. for that matter, you can do a search through the NCDC Storm Events Database. Just a note, this data only goes back to 1950, but you can search a broad range of days or just a single day to see how many reports of severe weather there were. Just as an example the Port Edwards Hail Storm from June 2007 not only gives you details on how many millions of dollars of damage was caused, but also provides more info on the weather conditions that day which lead up to the severe weather outbreak. Last but not least, I also stumbled upon satellite and radar images from 6/7/07 that show how things looked when the storms were raking their way through our area.
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